U.S. patent application number 14/243678 was filed with the patent office on 2014-10-16 for solar cell.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Taizo Masuda, Kenichi Okumura, Junya Ota. Invention is credited to Taizo Masuda, Kenichi Okumura, Junya Ota.
Application Number | 20140305504 14/243678 |
Document ID | / |
Family ID | 51685941 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140305504 |
Kind Code |
A1 |
Masuda; Taizo ; et
al. |
October 16, 2014 |
SOLAR CELL
Abstract
A high voltage output solar cell which is small in size and high
in power generation efficiency is provided. The solar cell is
provided with a p-type or n-type monocrystalline semiconductor
substrate (1) forming a power generation layer, a plurality of hole
collecting layers (2), electron collecting layers (3), and grooves
(7) provided inside of the semiconductor substrate (1) contiguous
to a back surface which faces a light receiving surface of the
semiconductor substrate (1), hole collecting layers (2) and
electron collecting layers (3) being provided between adjoining
grooves (7) and hole collecting layers (2) and electron collecting
layers (3) being provided sandwiching grooves (7), and interconnect
layers (8) which connect hole collecting layers (2) and electron
collecting layers (3) sandwiching grooves (7), the grooves (7)
being formed from the back surface side toward the inside of
semiconductor substrate (1).
Inventors: |
Masuda; Taizo; (Yokohama-shi
Kanagawa-ken, JP) ; Okumura; Kenichi; (Gotenba-shi
Shizuoka-ken, JP) ; Ota; Junya; (Susono-shi
Shizuoka-ken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Masuda; Taizo
Okumura; Kenichi
Ota; Junya |
Yokohama-shi Kanagawa-ken
Gotenba-shi Shizuoka-ken
Susono-shi Shizuoka-ken |
|
JP
JP
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi Aichi-ken
JP
|
Family ID: |
51685941 |
Appl. No.: |
14/243678 |
Filed: |
April 2, 2014 |
Current U.S.
Class: |
136/261 ;
136/252 |
Current CPC
Class: |
Y02P 70/50 20151101;
Y02P 70/521 20151101; H01L 31/1804 20130101; Y02E 10/547 20130101;
H01L 31/0475 20141201; H01L 31/035281 20130101; H01L 31/0682
20130101 |
Class at
Publication: |
136/261 ;
136/252 |
International
Class: |
H01L 31/0236 20060101
H01L031/0236 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2013 |
JP |
2013-083757 |
Claims
1. A solar cell comprising: a p-type or n-type monocrystalline
semiconductor substrate which forms a power generation layer, a
plurality of hole collecting layers, electron collecting layers,
and grooves which are provided inside of said semiconductor
substrate contiguous to a back surface which faces a light
receiving surface of said semiconductor substrate, said hole
collecting layers and said electron collecting layers being
provided between adjoining grooves and said hole collecting layers
and said electron collecting layers being provided sandwiching said
grooves, and interconnect layers which connect said hole collecting
layers and said electron collecting layers sandwiching said
grooves, said grooves being formed from said back surface side
toward the inside of said semiconductor substrate.
2. The solar cell according to claim 1, further comprising high
concentration doped layers with doped concentrations of
predetermined values or more formed in accordance with the
conductivity types of said power generation layers between the
light receiving surface of said semiconductor substrate and the
bottoms of said grooves.
3. The solar cell according to claim 1, further comprising low
concentration doped layers with carrier concentrations lower than
carrier concentrations of said power generation layer, said low
concentration doped layers being formed between the light receiving
surface of said semiconductor substrate and the bottoms of said
grooves.
4. The solar cell according to claim 1, further comprising
diffusion layers with different conductivity types formed between
said adjoining grooves at a light receiving surface side of said
semiconductor substrate.
5. The solar cell according to claim 1, further comprising
insulating films formed at surfaces of said grooves.
6. The solar cell according to claim 1, wherein said grooves are
formed to a depth of three-fourth of a thickness of said
semiconductor substrate.
7. The solar cell according to claim 1, wherein said semiconductor
substrate is formed using Si, Ge, C, SiGe, and SiC as a material.
Description
FIELD
[0001] The present invention relates to a solar cell, more
particularly relates to a solar cell which can form a high voltage
output by a single cell.
BACKGROUND
[0002] In general, the output voltage of a solar cell is low.
Therefore, usually, the practice is to serially connect a plurality
of solar cells to obtain the desired output voltage. Japanese
Patent Publication No. 2006-156663 describes a solar battery which
connects a plurality of solar cells in series to obtain a high
voltage output. On the other hand, when a plurality of solar cells
cannot be arrayed, that is, when the installation area is small
such as on the roof of a vehicle, and it is necessary to place a
solar battery to obtain a high voltage output, a single
commercially available solar cell has been separated into a
plurality of small cells and the separated small cells have been
connected in series to try to obtain the desired high voltage
output.
[0003] FIG. 10A shows a commercially available single solar cell
100 (156 mm.times.156 mm) with an output voltage of 0.7V. If
physically separating this solar cell 100 into, for example, 12
small cells 200, 200 . . . and using interconnects such as shown in
FIG. 10B to connect them in series, it is possible to construct a
solar cell panel with a 0.7.times.12=8.4V output voltage. The solar
cell 100 is cut into individual small cells mechanically using a
circular blade.
[0004] However, the solar cell panel which is configured such as in
FIG. 10B has the following problems: That is, a) there are spaces
between the adjoining small cells 200, so it is not possible to
effectively utilize that portion of the solar energy. When
producing the solar cell panel (when laminating it), the protective
material (EVA or rubber or other such material) which surrounds the
cells contracts by heat, so it is necessary to provide spaces
between adjoining cells. If there were no spaces, the adjoining
cells would interfere with each other and the cells would be
damaged. For this reason, the space between cells is for example
made 2 mm or so. If this space is not provided, production of solar
cell panels with a low reject rate becomes difficult.
[0005] Furthermore, b) physically cutting a single solar cell into
a plurality of small cells 200 causes the cell area to drop and the
amount of power generation to fall by that amount, so the cost of
manufacturing a solar cell panel for obtaining the desired output
power increases. The cell is cut mechanically by using a circular
blade, so the cell area falls by at least the blade thickness (tens
of .mu.m). The greater the number of parts separated into, the
greater that effect.
[0006] Further, c) as shown in FIG. 11, when connecting the small
cells 200 in series, the individual cells deviate in position and
the appearance becomes poor. As explained above, when producing a
solar cell panel, the protective material which surrounds the cells
contracts under heat. Along with that contraction, the cells also
end up moving somewhat. The heat contraction occurs in random
directions, so the cells deviate in position. The larger the number
of cells which are connected, the more noticeable the positional
deviation of the cells which have moved slightly. The appearance
becomes extremely poor.
SUMMARY
[0007] As explained above, in a solar cell panel which is obtained
by separating a single solar cell into a plurality of cells and
connecting them in series to obtain a high voltage output, there
are the problems that due to the drop in the efficiency of
utilization of solar energy, the physical reduction in the cell
areas, etc., the cost for obtaining a predetermined amount of power
generation increases and the appearance becomes poor. Therefore,
the object of the present invention is to provide a solar cell
which can give a high voltage output without separating the solar
cell.
[0008] To achieve the above object, in a first aspect of the
present invention, there is provided a solar cell which is provided
with a p-type or n-type monocrystalline semiconductor substrate
which forms a power generation layer, a plurality of hole
collecting layers, electron collecting layers, and grooves which
are provided inside of the semiconductor substrate contiguous to a
back surface which faces a light receiving surface of the
semiconductor substrate, the hole collecting layers and the
electron collecting layers being provided between adjoining grooves
and the hole collecting layers and the electron collecting layers
being provided sandwiching the grooves, and interconnect layers
which connect the hole collecting layers and the electron
collecting layers sandwiching the grooves, the grooves being formed
from the back surface side toward the inside of the semiconductor
substrate.
[0009] In the solar cell of the first aspect, high concentration
doped layers with doped concentrations of predetermined values or
more may be formed in accordance with the conductivity types of the
power generation layer between the light receiving surface of the
semiconductor substrate and the bottoms of the grooves. Further,
low concentration doped layers with carrier concentrations lower
than the carrier concentrations of the power generation layer may
be formed between the light receiving surface of the semiconductor
substrate and the bottoms of the grooves. Furthermore, a light
receiving surface side of the semiconductor substrate may be formed
with diffusion layers with different conductivity types between the
adjoining grooves.
[0010] Still further, insulating films may be formed at surfaces of
the grooves. The grooves have to have a depth of three-fourths of
the thickness of the semiconductor substrate. The power generation
layer may be formed using Si, Ge, C, SiGe, and SiC as a
material.
[0011] In the solar cell of the present invention, it is possible
to obtain a high voltage output without separating a cell into a
plurality of small cells. For this reason, it is possible to
generate power while utilizing all of the light receiving area
inherently possessed by the cell without detracting from it, so it
is possible to obtain a high power generation efficiency. Further,
along with this, the cost of manufacture of the solar cell panel
decreases. Furthermore, since a single cell can be used to achieve
a high voltage output, it becomes possible to form a beautiful
appearance solar cell panel free of the problems of positional
deviation of cells which occurs when arranging a plurality of cells
together.
[0012] Note that, the grooves which separate the solar cell into a
plurality of regions never reach the front surface of the solar
cell. Therefore, non-separated regions remain between the solar
cell surface and bottom of the grooves, but these parts are, for
example, provided with high concentration impurity doped layers,
low carrier concentration layers, or diffusion layers of different
conductivity types at the left and right of the non-separated
regions whereby movement of carriers between regions through the
non-separated regions is prevented and a drop in power generation
efficiency is prevented. Further, by providing insulating films on
the surfaces of the grooves, even when the solar cell is bent due
to the requirements of the installation location etc.,
short-circuits due to contact of adjoining regions with each other
can be prevented.
[0013] The present invention may be more fully understood from the
description of the preferred embodiments according to the invention
as set forth below, together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view of a back surface electrode
type solar cell.
[0015] FIG. 2 is a cross-sectional view of a solar cell according
to an embodiment of the present invention.
[0016] FIG. 3 is a plan view of a solar cell which is shown in FIG.
2.
[0017] FIG. 4 is a plan view of a modification of a solar cell
which is shown in FIG. 1.
[0018] FIG. 5 is a cross-sectional view of a solar cell according
to another embodiment of the present invention.
[0019] FIG. 6 is a view which shows enlarged part of a solar cell
which is shown in FIG. 5.
[0020] FIG. 7 is a cross-sectional view which shows a modification
of the embodiment which is shown in FIG. 5.
[0021] FIG. 8 is a cross-sectional view of a solar cell according
to still another embodiment of the present invention.
[0022] FIG. 9 is a view which explains the advantageous effect of
the solar cell which is shown in FIG. 8.
[0023] FIG. 10A is a plan view of a conventional solar cell.
[0024] FIG. 10B is a schematic view which shows a high output solar
cell panel which is comprised of the solar cells of FIG. 10A.
[0025] FIG. 11 is a view which shows positional deviation of cells
in the solar cell panel which is shown in FIG. 10B.
DESCRIPTION
[0026] Below, various embodiments of the present invention will be
explained with reference to the drawings. Note that, in the figures
which are shown below as a whole, the same reference notations show
the same or similar components and overlapping explanations are not
given. Furthermore, the figures are meant only for explaining the
present invention. Therefore, the sizes of the components in the
figures do not correspond to the actual scale.
First Embodiment
[0027] The structure of a back surface electrode type solar cell 10
according to a first embodiment of the present invention will be
explained with reference to FIGS. 1 and 2. FIG. 1 is a
cross-sectional view of a solar cell which for example provides a
power generation layer 1 which is comprised of an n-type
monocrystalline semiconductor substrate of Si with a plurality of
pairs of p.sup.+ diffusion layers 2 which function as hole
collecting layers and n.sup.+ diffusion layers 3 which function as
electron collecting layers and provide the diffusion layers 2, 3
with positive electrodes 4 or negative electrodes 5. In this state
of solar cell, in the past the solar cell was physically cut along
the dividing lines 6 to form a plurality of small cells with equal
areas. These were connected in series to form a solar cell panel
which provided a high voltage output.
[0028] As opposed to this, the solar cell 10 of the present
embodiment, as shown in FIG. 2, is characterized by providing
grooves 7 which do not reach the front surface of the power
generation layer at the positions of the dividing lines 6 to
thereby partition and physically separate the power generation
layer 1 into a plurality of equal volume regions 1a. The grooves 7
are formed leaving at least about one-fourth of the layer thickness
of the power generation layer 1 from the solar cell surface (light
receiving surface). To completely separate the adjoining regions
1a, 1a, the grooves 7 are preferably formed up to close to the
front surface of the power generation layer 1, but to secure the
mechanical strength of the solar cell 10 as a whole, it is
necessary to leave a certain extent of non-separated regions, for
example, about one-fourth of the layer thickness of the power
generation layer 1.
[0029] In the illustrated embodiment, for example, in a solar cell
which overall has a size of 156 mm.times.156 mm, when the thickness
(T) of the power generation layer 1 is 150 .mu.m, the depth (t) of
the grooves 7 from the back surface is made about 100 .mu.m and the
width (w) is made about 1 .mu.m.
[0030] In FIG. 2, 8 show interconnect layers which use Al etc. as a
material. They are provided to serially connect the regions 1a of
the power generation layer 1 by serially connecting the positive
electrodes and negative electrodes 5 between the adjoining regions
1a, 1a. Reference numeral 9 shows takeout electrodes for connection
with other solar cells or devices. The positive electrodes 4,
negative electrodes 5, interconnect layers 8, and takeout
electrodes 9 are, for example, formed using Al as a material.
[0031] The grooves 7 can be easily formed by for example dry
etching the solar cell 10 in the state of FIG. 1 from the back
surface side (opposite side to light receiving surface). For
forming the etching pattern, for example, a lithographic process
may be utilized. Note that, the regions (non-separated regions)
which remain unseparated between the bottoms of the grooves 7 and
light receiving surface of the power generation layer 1 are
preferably a single monocrystal, but the regions may also be
connected in a polycrystalline state.
[0032] FIG. 3 is a plan view which views the solar cell 10
according to the present embodiment from the back surface side, but
here the positive and negative electrodes 4, 5, interconnect layers
8, and takeout electrodes 9 are omitted from the illustration. As
shown in FIG. 3, in the solar cell 10 of the present embodiment,
the plurality of regions 1a which have pairs of p.sup.+ diffusion
layers 2 and n.sup.+ type diffusion layers 3 are delineated by the
grooves 7. The grooves 7, as shown in the figure, are formed
cutting across the horizontal width of the solar cell 10. Further,
five are formed in parallel in the direction of the vertical width.
For this reason, the solar cell 10 is separated into six regions of
substantially 25 mmX156 mm size.
[0033] While not shown in FIG. 3, the p.sup.+ diffusion layers 2
and n.sup.+ diffusion layers 3 which adjoin each other through the
grooves 7 are connected by the interconnects 8 (see FIG. 2),
whereby six regions 1a are connected inside one solar cell 10. As a
result, for example, 0.7.times.6=4.2V of output can be obtained. In
this way, in the solar cell of the present embodiment, it is
possible not to physically cut the cell to separate it and to
obtain a high voltage output by the size of a single cell.
[0034] Note that, FIG. 2 corresponds to a cross-section on the line
X-X of FIG. 3. Further, in general, sometimes the front surface of
the power generation layer 1 (light receiving surface) is provided
with a passivation layer, reflection prevention layer, etc., but
these are omitted since they have no direct bearing in the
explanation of the configuration of the present invention.
[0035] FIG. 4 is a schematic view which shows a modification of the
first embodiment of the present invention. This solar cell 20 is an
example where a solar cell is separated by a plurality of vertical
and horizontal grooves 7 into equal areas. If connecting the
adjoining regions 1b, 1b separated by the grooves 7 so that the
p.sup.+ diffusion layers 2 and the n.sup.+ diffusion layers 3 are
connected in series, it is possible to form a high voltage output
in accordance with the number of the connected regions. Note that,
there are various patterns for formation of grooves 7. The
invention is not limited to those which are shown in FIGS. 3 and
4.
[0036] In the above way, in the solar cell according to the first
embodiment of the present invention, unlike the conventional
device, high voltage output is achieved without physically
separating one cell into a plurality of small cells, so it is
possible to effectively utilize solar energy without light
receiving loss. Furthermore, it is not necessary to physically
arrange a plurality of small cells to form a high voltage output
panel, so there is no deterioration of appearance due to positional
deviation.
Second Embodiment
[0037] In the solar cell according to the first embodiment of the
present invention which is shown in FIG. 2, the adjoining regions
1a, 1a (or 1b, 1b) were separated by grooves 7, but non-separated
regions remained between the bottoms of the grooves 7 and the light
receiving surface of the power generation layer 1 so these were
electrically connected. For this reason, while slight, carriers
moved between adjoining regions through these non-separated
regions. The adjoining regions 1a, 1a of the present invention are
connected in series, so unless the balance of current (carriers) is
constant at the different regions, the smallest current in the
regions will become an influencing factor and as a result the
overall amount of power generation will fall. The solar cell
according to the second embodiment was made in consideration of
this point and is characterized by provision of a mechanism which
limits the carrier movement between adjoining regions.
[0038] FIG. 5 is a cross-sectional view of a solar cell according
to the second embodiment of the present invention. The solar cell
30 of the present embodiment, as shown in the figure, provides the
non-separated regions between adjoining regions with high
concentration doped layers 12 of n-type or p-type impurities so as
to suppress carrier movement between adjoining regions and prevent
a drop in the amount of power generation. The high concentration
doped layers 12 have depths of extents reaching the bottoms of the
grooves 7. Further, the widths are preferably not more than the
widths of the grooves 7. The doped concentrations may be made
values higher than the power generation layer 1 when the high
concentration doped layer 12 has a conductivity type the same as
the power generation layer 1 and may be made certain extents or
more, for example, 1.times.10.sup.15 cm.sup.-3 or more, when the
high concentration doped layer 12 has a conductivity type reverse
from the power generation layer 1.
[0039] Further, the high concentration doped layer 12, as shown in
FIG. 6, may be formed to have a set of a p-type region 12a and
n-type region 12b. Furthermore, it is desirable to provide high
concentration doped layers 12 for all of the grooves 7 of the solar
cell 30, but if there is at least one high concentration doped
layer 12 present, there is an effect of suppression of carrier
movement between the adjoining regions 1a, 1a.
[0040] Note that, in the structure of FIG. 5, instead of providing
the high concentration doped layers 12, it is also possible to
provide low carrier concentration layers (i-layer). The low carrier
concentration layers have a lower carrier concentration than the
carrier concentration of the power generation layer 1. The lower
the carrier concentration, the higher that part in resistance value
and the greater the effect of prevention of carrier movement. The
depths, widths, etc. of the low carrier concentration layers are
the same extents as the high concentration doped layers 12 of FIG.
5.
[0041] A solar cell 30 which has the high concentration doped
layers 12 or low carrier concentration layers is formed, for
example, by forming between the front surface and back surface side
of the power generation layer 1 a protective layer constituted by a
SiO.sub.2 layer by plasma CVD, etching the parts of the SiO.sub.2
layer for forming the high concentration doped layers 12 etc. into
patterns by utilizing a photolithography process etc., then heating
this in a sealed container which is filled with n-type or p-type
dopant gas. For the dopant gas, when the layers which are formed
are the n-type, phosphine is utilized, while when the layers are
the p-type, diborane etc. are utilized. The doping concentration
and the diffusion depth can be made the desired values by
controlling the heating temperature and gas concentration. When
forming a low carrier concentration layer, doping gas which has a
polarity reverse to the power generation layer is utilized. The
high concentration doped layer 12 or low carrier concentration
layer may be formed before forming the grooves 7 or after forming
the grooves 7.
[0042] FIG. 7 is a view which shows a modification of the second
embodiment. In this solar cell 30', in the regions 1a which are
separated by the grooves 7, the surface parts of the adjoining
regions are provided with p.sup.+ type diffusion layers 13a and
n.sup.+ type diffusion layers 13b. The p.sup.+ type diffusion
layers 13a and n.sup.+ type diffusion layers 13b have depths of the
same extents as the depths of the parts at which the adjoining
regions 1a are connected (non-separated regions). In this solar
cell 30', energy barriers are formed at the non-separated regions
so as to prevent carrier movement between adjoining regions, so a
drop in the amount of power generation is prevented.
Third Embodiment
[0043] FIG. 8 is a cross-sectional view of a solar cell 40
according to a third embodiment of the present invention. The solar
cell 40 of the present embodiment provides the solar cell 30 which
is shown in FIG. 5 characterized in that the surfaces of the
grooves 7 are formed with insulating films 7a. The insulating films
7a, for example, use as a material glass which contains boron or
phosphorus, SiO.sub.2, SiN.sub.x, a resin, etc.
[0044] FIG. 9 shows the case of, for example, installing the solar
cell 10 which is shown in FIG. 2 etc. on the roof of a vehicle. The
roof of a vehicle is formed into a curved surface rather than a
flat surface. If forming the solar cell 10 into a roof shape so as
to install it there, the amount of deformation at the back surface
side will be greater than at the front surface side and the
adjoining regions 1a will sometimes end up contacting each other at
the back surface side. In a back surface electrode type solar cell,
power is generated mainly near the back surface, so if the
adjoining regions contact each other near the back surface,
short-circuited states will be caused and as a result the amount of
power generation will greatly fall or no power at all will be
generated any longer. In the solar cell 40 of the embodiment which
is shown in FIG. 8, such a situation is prevented by forming
insulating films 7a at the surfaces of the grooves 7.
[0045] The insulating films 7a can, for example, be formed by the
following method: That is, when the insulating films 7a are glass
which contain boron or phosphorus, the glass layers are formed by
coating liquid solid layer diffusion sources on the surfaces of the
grooves 7 and heat treating them to cause the organic binder to
evaporate and thereby be removed. Further, when the insulating
films 7a are SiO.sub.2, the etching surfaces are heat treated in a
water vapor atmosphere so as to form SiO.sub.2 films on the
surfaces of the grooves 7. When the insulating films 7a are
SiN.sub.x, plasma CVD is used to deposit and form SiN.sub.x on the
etching surfaces. When the insulating films 7a are resin films,
resin which is dissolved in an organic solvent is coated on the
etching surfaces, then these are heated to evaporate away the
organic solvent and form resin layers on the surfaces of the
grooves 7.
[0046] Note that, in the embodiment which is shown in FIG. 8, high
concentration doped layers 12 were provided between the grooves 7
and the surface of the power generation layer 1, but the present
embodiment which forms the insulating films on the surfaces of the
grooves 7 can of course be applied to any of the solar cells
according to the present invention which are for example shown in
the other figures.
[0047] Further, in the above embodiments, the example was shown of
use of Si as the material for the power generation layers which
form the solar cells, but the present invention may be similarly
worked by Ge, C, SiGe, SiC, etc. as well.
[0048] Furthermore, in the above embodiments, a single solar cell
was provided with a plurality of grooves 7, but the present
invention can also be worked by providing a single solar cell with
a single groove. For example, by forming a single groove 7 at the
center in the vertical direction or horizontal direction of a cell,
it is possible to form a device which gives double the output
voltage of an ordinary solar cell. Therefore the present invention
can also be applied to the case of a single groove 7.
[0049] While the invention has been described by reference to
specific embodiments chosen for purposes of illustration, it should
be apparent that numerous modifications could be made thereto, by
those skilled in the art, without departing from the basic concept
and scope of the invention.
[0050] This application claims the benefit of JP Application No.
2013-83757, the entire disclosure of which is incorporated by
reference herein.
* * * * *